Electrical problems C210RPT

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TomGold
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Electrical problems C210RPT

Unread post by TomGold » Sun Sep 15, 2019 11:08 am

C210 RTP
While in flight a high pitch whine suddenly started on the audio system.
The pitch was engine speed dependent, also it got much louder on final approach and on the ground, also louder when heavy loads were switched on.
Turning off the alternator stopped the noise.

Changed the alternator, noise gone, all good.
Next flight, in flight the power fails, return to base but on recycling the alternator, the power returns.
Has happened before so changed the voltage control unit.

Next IF flight all good, 1 hr into the flight the whine started again.

Fly VF back to base and investigate.
Checked all wiring and all possible oxidized contacts, clean up all terminals.
No effect.
Take Oscilloscope and monitor the board 24 volts.
See normal ripple but every cycle a high negative transition.

This could be a broken diode.

The question is, given the history of power outage, now the third alternator, 2nd voltage control unit, what could be the underlining cause of the problem.

It is not clear if the power outage on the Alternator are linked but their is something rather strange happening which for an IF aircraft can be a little disturbing.
Any ideas of what could be the underlining problem?
Any leads or thoughts would be very valuable in fault finding.
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jimdavis
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Re: Electrical problems C210RPT

Unread post by jimdavis » Sun Sep 15, 2019 11:20 am

Whenever I have had the same symptoms it was an alternator problem, but it seems to go deeper than that now.

My take is that this is not an IF aeroplane until you find the problem.

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Re: Electrical problems C210RPT

Unread post by homebuilt » Sun Sep 15, 2019 12:13 pm

Suggest you check all the cabling from and to the alternator for chafe / internal breaks. It sounds like you are getting pick-up from one of your main feed cables either shorting or flashing inside the insulation. Could also try running a new cable lying loosely and not fitted into the loom just to make sure you are not getting pick-up from one of the other power cables in the loom. Ps. also check that the alternator is well grounded onto the engine. I am not an aircraft tecchie but have had years working on motor vehicles so hope the boffins don't punish me for my suggestions.
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Re: Electrical problems C210RPT

Unread post by davebutler » Sun Sep 15, 2019 1:07 pm

Agree with homebuilt, had a similar issue with a PA28 many years ago.
Never did find the actual fault but maint guys replaced some wiring, problem solved.
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Re: Electrical problems C210RPT

Unread post by Ugly Duckling » Sun Sep 15, 2019 1:26 pm

Is the battery cranking the engine properly?
If it looks lazy:
1. Give it a constant current charge as per the maintenance manual.
2. Check the battery positive cables, master relay, battery earth cable, engine / engine mount & engine mount / firewall earth cable.

May pay to use long leads on the multimeter and check voltage drop on positive and negative circuits to the starter motor while cranking with the mags off.
[-X Remember [-X Clear Prop!!! [-X

The battery is a capacitor and should soak up ripple and spikes. If there is any connection which is a higher resistance than normal the battery will stop soaking up the noise.
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Re: Electrical problems C210RPT

Unread post by TomGold » Wed Sep 18, 2019 10:08 am

Thanks guys for your suggestions, prior to sending out the blog, we checked the grounding and all the connectors, plus and minus, unscrewed all, cleaned and polished each one, engine side.
It is possible the problem comes from an intermittent continuity.
My question however revolves round, what can lead to a diode going short.
One of the theories is a high voltage spike which could come from something inductive.
There are only a few places, Motors: Fuel pumps, Starter, the high current relays and the Bendix. which could create a high voltage spike.
Bearing in mind the problem occurred in flight, after start, its hard to include these.

The only high current device we switched on was prop de-iceing.
Another offered theory is the main Alternator switch is faulty or the wiring is?
Maybe a breaking contact on the prop slip rings? (not inductive though).
Any other ideas. We are also using an oscilloscope and multimeters to help observe.

Appreciate your inputs.
Thank
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Re: Electrical problems C210RPT

Unread post by Oldlae » Wed Sep 18, 2019 10:30 am

You have a Diode gone bad in the rectifier part of the voltage regulator.
If it was mine I would whip the Alternator off and take it to your local auto electrician to fit a new voltage regulator.
If the aircraft has a separate voltage regulator, even easier, purchase a replacement.
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Re: Electrical problems C210RPT

Unread post by southside » Wed Sep 18, 2019 6:27 pm

Oldlae wrote:
Wed Sep 18, 2019 10:30 am
You have a Diode gone bad in the rectifier part of the voltage regulator.
If it was mine I would whip the Alternator off and take it to your local auto electrician to fit a new voltage regulator.
If the aircraft has a separate voltage regulator, even easier, purchase a replacement.
Tony
Maybe if you bomb around the cabbage patch on the odd Sunday in your Jabbi you can do that. But you can't do this on a ZS aircraft. What 8130 is your local auto electrician going to issue for your engine logbook?Otherwise you would have everyone and there tjommas changing your wing bolts and engine mount rubbers on the weekend in exchange for a case of beer.

Aside from the electrical issue, the OP is a brave man operating a single engine piston in IMC. By virtue of the fact that he is flying the aircraft IF one would conclude that he operates in IMC. I am not brave enough for that. Its not allowed in commercial ops and IMHO should not be allowed at all. Even in a multi piston...I want full weather radar and full anti-ice sytems before I go wandering into the clagg.
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Re: Electrical problems C210RPT

Unread post by Chalkie » Wed Sep 18, 2019 7:16 pm

southside wrote:
Wed Sep 18, 2019 6:27 pm
Oldlae wrote:
Wed Sep 18, 2019 10:30 am
You have a Diode gone bad in the rectifier part of the voltage regulator.
If it was mine I would whip the Alternator off and take it to your local auto electrician to fit a new voltage regulator.
If the aircraft has a separate voltage regulator, even easier, purchase a replacement.
Tony
Maybe if you bomb around the cabbage patch on the odd Sunday in your Jabbi you can do that. But you can't do this on a ZS aircraft. What 8130 is your local auto electrician going to issue for your engine logbook?Otherwise you would have everyone and there tjommas changing your wing bolts and engine mount rubbers on the weekend in exchange for a case of beer.

Aside from the electrical issue, the OP is a brave man operating a single engine piston in IMC. By virtue of the fact that he is flying the aircraft IF one would conclude that he operates in IMC. I am not brave enough for that. Its not allowed in commercial ops and IMHO should not be allowed at all. Even in a multi piston...I want full weather radar and full anti-ice sytems before I go wandering into the clagg.
Two things: I agree the rectifier is most likely the cause of the problem and note, this unit is separate to the voltage regulator.

SS: statistically a twin engine aircraft has twice as much chance of an engine failure compared to a single and usually (on the highveld) the other engine takes you to the scene of the crash.

"I am not brave enough for that. Its not allowed in commercial ops and IMHO should not be allowed at all."

AFAIK it is legal and safe, just as safe as a twin with a SE ceiling of less than 8000' DA.
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Re: Electrical problems C210RPT

Unread post by southside » Wed Sep 18, 2019 7:46 pm

Hi Chalkie. Your opinion is noted. But as you say, usually it will take you to the crash site. Just after takeoff or before landing the odds are stacked against you. That is why I said 'even in a multi piston' because it is still not ideal. But in the cruise, even on the highveld, most light twins will maintain comfortably on one engine with the dead one feathered. I have tried and tested it. At MAUW you will be pushing it though. I will still rather be in a twin in the clagg and have an engine go than be in a single. Worst case is you realise you will not be able to be above vmca and execute a forced landing as per a single.

If your multi skills are current, would you want to be in the cruise at 8000ft over the jhb cbd in IMC in a single or a twin? As mentioned, if this happened just after takeoff, even in VMC, your finger needs to be properly out just so that you can stand a chance of surviving the inevitable crash landing.

With regards to SE piston being legal, it is not legal as per the CAR's in IMC. Under Part 91 it is legal, but not smart IMHO.

But we digress. Back to topic.
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Re: Electrical problems C210RPT

Unread post by TomGold » Thu Sep 19, 2019 8:57 am

jimdavis wrote:
Sun Sep 15, 2019 11:20 am
Whenever I have had the same symptoms it was an alternator problem, but it seems to go deeper than that now.

My take is that this is not an IF aeroplane until you find the problem.

jim
As you may have seen in my original blog on this topic, the moment we noticed the problem we went VF which is the thing to do.

New thoughts surround the fact that a diode has gone and what could lead to this.
Often a high voltage surge.
Inductive loads, particularly if their connectors are ohm-ish can cause a spike.
Now looking at connectors to inductive loads, Pneumatic pump, anything that can cause a surge.
The aircraft is over 30 years with original wiring so many connectors "could" have creating resistance problems.
Just further thoughts on this challenging problems.
T
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Re: Electrical problems C210RPT

Unread post by jimdavis » Thu Sep 19, 2019 9:04 am

Tom, do remember to let us all know when you do find the problem. You have a some very interested followers!

Jim
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Re: Electrical problems C210RPT

Unread post by TOFFS » Thu Sep 19, 2019 10:06 am

Check that the earth strap between the engine and airframe is there and that it is connected.

The engine is isolated from the airframe through the Lord mounts; if you don't have correct bonding your engine is using engine control cables etc as an earth return.

This is a simple system and if you have replaced what could break, then it is usually something as basic as a bonding strap left off.

I'm not too far away from CT if you'd like me to have a look.
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Re: Electrical problems C210RPT

Unread post by Oldlae » Thu Sep 19, 2019 10:09 am

Chalkie wrote:
Wed Sep 18, 2019 7:16 pm
southside wrote:
Wed Sep 18, 2019 6:27 pm
Oldlae wrote:
Wed Sep 18, 2019 10:30 am
You have a Diode gone bad in the rectifier part of the voltage regulator.
If it was mine I would whip the Alternator off and take it to your local auto electrician to fit a new voltage regulator.
If the aircraft has a separate voltage regulator, even easier, purchase a replacement.
Tony
Maybe if you bomb around the cabbage patch on the odd Sunday in your Jabbi you can do that. But you can't do this on a ZS aircraft. What 8130 is your local auto electrician going to issue for your engine logbook?Otherwise you would have everyone and there tjommas changing your wing bolts and engine mount rubbers on the weekend in exchange for a case of beer.

Aside from the electrical issue, the OP is a brave man operating a single engine piston in IMC. By virtue of the fact that he is flying the aircraft IF one would conclude that he operates in IMC. I am not brave enough for that. Its not allowed in commercial ops and IMHO should not be allowed at all. Even in a multi piston...I want full weather radar and full anti-ice sytems before I go wandering into the clagg.
Two things: I agree the rectifier is most likely the cause of the problem and note, this unit is separate to the voltage regulator.

SS: statistically a twin engine aircraft has twice as much chance of an engine failure compared to a single and usually (on the highveld) the other engine takes you to the scene of the crash.

"I am not brave enough for that. Its not allowed in commercial ops and IMHO should not be allowed at all."

AFAIK it is legal and safe, just as safe as a twin with a SE ceiling of less than 8000' DA.


I was under the impression that you live in South Africa, ........and you have never heard of a 'shade tree mechanic' ?
Just change the voltage regulator, and I'm sure you will be good to go.
Tony
Retired Licenced AME with 50 years under my belt.

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Re: Electrical problems C210RPT

Unread post by TomGold » Sun Sep 22, 2019 12:17 pm

Thank you everyone for the hints and the ideas,
I would like to clear up a few issues which have come up during the very valuable discussion.

I live in Cape Town 6 months of the year, the other in Europe where this aircraft is located. so thanks TOFFS for the offer to come look, rather a long way.
As right from the start, mentioned, as soon as we noticed the problem we flew VF.

Yes it is with almost 99% certainty, a diode and we have asked for a guarantee replacement, as we all know, it all takes time and on another forum, there are many comments about how unreliable the diodes are on what amounts to a ford car Alternator.

. The core question is what is causing the diodes to fail.

We have already changed the voltage regulator and have spent a lot of time cleaning up all the positive and negative connections to the various places.

One thought is, a high dynamic pulse can be caused by an inductive source, like a motor or relays, that is why we are concentrating on all connections in this area. e.g. Undercarriage Pneumatic pump driver motor, etc.

The tip about the grounding of the engine (once again TOFFS) is very valuable and we will look into this but since the alternator is mounted on the engine and the negative of the output DOES go to ground, I suspect this should be ok.
I measured the DC resistance and it was fine.
Dynamic resistance even here could be a cause so worth pursuing.
So much for the moment, as soon as we know what the reason is, we will give more feedback.
Thanks again, very valuable.
T

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